1. Field of the Invention
This invention generally relates to integrated circuit (IC) and liquid crystal display (LCD) fabrication and, more particularly, to a method for electroforming metal wiring and related structures.
2. Description of the Related Art
In current integrated circuit and display applications, physical vapor deposition (PVD) aluminum/copper/silicon alloys are used to form interconnects and electrically conductive wires (traces) on the various circuit layers. Generally, these wires are formed on a scale of magnitude in the region of 1 to 1000 microns. These wires are patterned subtractively, by etching a conformal deposition of metal through a photoresist mask. Alternatively, copper damascene process is used, which forms a patterned trench structure, fills the trench with metal, and polishes excess metal deposited overlying the trench. However, these subtractive processes limit the shapes into which the resultant metal structures can be formed. For example, it is difficult to form a metal structure that is re-entrant or one with an intentional overhang; a structure where the top cross-sectional area is greater than the bottom cross-sectional area.
On a vastly different scale, on the order of a millimeter, printer circuit board (PCB) processes form multi-layered boards with electrically conductive metal wires. Issues of chemical compatibility, substrate material consistency, and the rigorous exclusion of contamination prevent the direct scaling of PCB metallization technology to ICs, displays, and advanced multi-chip modules (MCMs). The larger size of PCBs permits macroscopic processes such as direct printing and pattern transfer to be used. However, these macroscopic processes cannot be used for ICs and LCDs due to the severe dimensional tolerances involved.
The deposition of metals on large IC substrates requires the use large chamber, expensive/complicated atmosphere and temperature control equipment. Often the IC and LCD processes require the use of vacuum chambers. PCB processes, on the other hand, require less sophisticated equipment, such as baths and plating devices.
Advantageously, the successive use of PCB additive deposition processes permits the easy formation of microscopic metal structures containing enclosures. These enclosure structures can be filled with a second material such as an insulator, which then might form a coaxial transmission line or other such structure. These structures cannot be obtained easily using conventional subtractive technology, since a re-entrant structure must be formed, in order to close off the inner volume.
It would be advantageous if IC and LCD metal structures could be formed using an additive deposition process.
It would be advantageous if conventional PCB electroplating processes could be adapted to IC and LCD processes, to provide a low cost, low thermal budget solution for metal deposition.
It would be advantageous if electroless deposition processes could be adapted to IC and LCD processes.